Why are some properties listed at 3x their comps value?

[Ruben Kanya]

Doing some market analysis on a site such as realtor.com which includes comps and I noticed the odd times there will be a property listed at 3-4 times the median price (i.e. 200% above median) of the neighborhood (in respect to its comps). 

Will it even appraise for that value come time to sell? Is it fair to think that there is an opportunity to rehab a home and list it at that similar price? I doubt it... Any legitimate reasons to why it may be that high? Thanks!